Financial advisors are increasingly using passive, index-tracking ETFs to implement strategies that are just as active as what you'd find in the most aggressive mutual funds.

Some pairings just make sense -- Scarlett and Rhett, peanut butter and jelly, exchange-traded funds and index investing. But when the pairing is put into a different context -- a campy musical version of Gone with the Wind, or a PB&J-filled breakfast cereal -- it becomes a distinctly different thing. And that "different thing" is happening in the world of ETFs.

Financial advisors are increasingly using passive, index-tracking ETFs to implement strategies that are just as active as what you'd find in the most...